This invention relates to coal and more particularly to stabilized coal-oil-mixtures and process for the production thereof.
Known resources of coal and other solid carbonaceous fuel materials in the world are far greater than the known resources of petroleum and natural gas combined. Despite this enormous abundance of coal and related solid carbonaceous materials, reliance on these resources, particularly coal, as primary sources of energy, has been for the most part discouraged. The availability of cheaper, cleaner burning, more easily retrievable and transportable fuels, such as petroleum and natural gas, has in the past, cast coal to a largely supporting role in the energy field.
Current world events, however, have forced a new awareness of global energy requirements and of the availability of those resources which will adequately meet these needs. The realization that reserves of petroleum and natural gas are being rapidly depleted in conjunction with skyrocketing petroleum and natural gas prices and the unrest in the regions of the world which contain the largest quantities of these resources, has sparked a new interest in the utilization of solid carbonaceous materials, particularly coal, as primary energy sources.
As a result, enormous efforts are being extended to make coal and related solid carbonaceous materials equivalent or better sources of energy, than petroleum or natural gas. In the case of coal, for example, much of this effort is directed to overcoming the environmental problems associated with its production, transportation and combustion. For example health and safety hazards associated with coal mining have been significantly reduced with the onset of new legislation governing coal mining. Furthermore, numerous techniques have been explored and developed to make coal cleaner burning, more suitable for burning and more readily transportable.
Gasification and liquefaction of coal are two such known techniques. Detailed descriptions of various coal gasification and liquefaction processes may be found, for example, in the Encyclopedia of Chemical Technology. Kirk-Othmer, Third Edition (1980) Volume 11, pages 410-422 and 449-473. Typically, these techniques, however, require high energy input, as well as the utilization of high temperature and high pressure equipment, thereby reducing their widespread feasibility and value.
Processes to make coal more readily liquefiable have also been developed. One such process is disclosed in U.S. Pat. No. 4,033,852 (Horowitz, et al.). This process involves chemically modifying a portion of the surface of the coal in a solvent media, the effect of which renders the coal more readily liquefiable in a solvent than natural forms of coal, thereby permitting recovery of a liquefiable viscous product by extraction.
In addition to gasification and liquefaction, other methods for converting coal to more convenient forms for burning and transporting are also known. For example, the preparation of coal-oil and coal-aqueous mixtures are described in the literature. Such liquid coal mixtures offer considerable advantages. In addition to being more readily transportable than dry solid coal, they are more easily storable, and less subject to the risks of explosion by spontaneous ignition. Moreover, providing coal in a fluid form makes it feasible for burning in conventional apparatus used for burning fuel. Such a capability can greatly facilitate the transition from fuel oil to coal as a primary energy source.
Typical coal-oil and coal-aqueous mixtures and their preparation are disclosed in U.S. Pat. Nos. 3,762,887, 3,617,095, 4,217,109 and British Patent No. 1,523,193. Additionally, U.S. Pat. No. 4,101,293 discloses coal-oil mixtures prepared from the admixture of a preformed stabilizing emulsifier comprised of the reaction product of an ethylenically unsaturated acid, such as tall oil, with an alkali hydroxide or alkanol amine, with pulverized coal and oil. Similarily, British Patent application No. 2079784A discloses coal-oil suspensions prepared from admixing coal and fuel oil with a preformed stabilizer comprised of a partially amidated copolymer obtained by reacting a copolymer of a polymerizable, unsaturated hydrocarbon and maleic anhydride with a saturated or unsaturated aliphatic amine or salt thereof. U.S. Pat. No. 4,251,229 is an example of coal-oil mixtures stabilized with high molecular weight adducts of alkylene oxide and an alcohol, an amine, a carboxylic acid or phenol having at least three active hydrogens.
In addition, U.S. patent application Ser. No. 230,055 filed Jan. 29, 1981, discloses a process for the production of stabilized coal-oil mixtures wherein pulverized coal is admixed with oil, a polymerizable fatty acid ester, such as tallow, and a polymerization catalyst therefor, under polymerization reaction conditions, and a stabilizing agent-forming amount of a gelling agent, such as an alkali metal hydroxide or ammonium hydroxide. Furthermore, U.S. Pat. No. 4,306,883 discloses that stable coal-oil mixtures can be formed from high water content coal by mixing said coal with oil, a monomeric compound, such as tall oil, and a chemical surface treatment agent, heating the mixture to an elevated temperature, subjecting the coal-oil mixture to a condition of low shear to form a low sheared coal-oil mixture, subjecting the low sheared coal-oil mixture to a condition of high shear and admixing a gelling agent, such as, alkali metal hydroxide or ammonium hydroxide to form a stable coal-oil mixture in the form of a gel or thixotropic mixture.
Moreover, U.S. Pat. No. 4,304,573 and United States Government Report No. 2694 entitled "Fuel Extension by Dispersion of Clean Coal in Fuel Oil", all incorporated herein by reference, inter alia, disclose a chemical surface treatment technique for forming coal into a coal-oil mixture. In summary, according to this chemical treatment method, coal is first cleaned of rock and the like and pulverized to a fine size of about 48 to 300 mesh. The pulverized coal, now in the form of a water slurry, is then treated with a monomeric compound, usually in the presence of a liquid organic carrier, and reaction addivite. The chemical treatment of the coal is adapted to make the coal both hydrophobic and oleophilic. Coal particles so treated are readily separated from unwanted ash and sulfur using oil and water separation techniques. The coal, which is now substantially cleaned of ash and sulfur, is then preferably dried to a water content level suitable for further processing or recovery. The dried coal is thereafter formed into a coal-oil mixture, where it can again be subjected to a chemical surface treatment using additional additive. The coal-oil mixture is thereafter treated with a gelling agent to form the coal-oil mixture in the form of a stable mixture, typically gel or thixotropic. The coal-oil mixture product thus produced is advantageously non-settling and enjoys a dispersion stability normally difficult to achieve and maintain without frequent stirring, the addition of further additives or an inordinate amount of fine grinding. In addition, the mixture thus formed can be thixotropic, allowing for ready pumpability on subjection to shearing or pumping forces.
It will be seen that this afore-described chemical surface treatment technique, such as disclosed in U.S. Pat. No. 4,304,573 offers considerable advantages in providing coal as a useful energy source. Although the technique is attractive, it is still desirable to make the process even more advantageous. For example, it would be highly desirable if the amount of drying, which the cleaned coal is subjected to prior to forming the coal-oil mixture could be reduced, without adversely affecting the gel forming process. Such a decrease in drying would significantly improve the overall efficiency of the process, and advantageously would reduce or eliminate the need for burdensome and expensive drying equipment, such as large scale thermal dryers. The use of thermal drying equipment, e.g., is both expensive and time consuming, particularly in large scale coal processing operations. Thus, the necessity for the use of drying equipment could seriously detract from an otherwise attractive process.
While many of these aforementioned procedures produce excellent stabilized coal-oil mixtures, improved formulations and procedures for the production thereof are still desirable, particularly those formulations and procedures providing high solids, i.e., high coal content mixtures, prepared from simple, cost reduced processes.